Grain tanks of combines commonly have an associated unloader conveyor operable for conveying grain from the grain tank to another location such as to a grain truck or wagon. An unloader conveyor typically includes an elongate, enclosed tubular housing containing a helical auger and is oriented horizontally or at a small acute angle to horizontal. The unloader conveyor is typically pivotally supported in cantilever relation by a lower end of an upstanding or vertical lower unloader conveyor section including an inlet opening disposed in or adjacent to the grain tank. The unloader conveyor is typically pivotable between a stored position extending along the combine, and a sidewardly extending unloading position. The unloader can be of any length, but will typically have a length sufficient to extend just beyond the end of a header of the combine. Grain tanks additionally typically include at least one grain tank conveyor including an auger adjacent to the bottom of the grain tank and extending into the inlet opening of the lower unloader conveyor for conveying grain into the unloader.
After use, if the unloader is not cleaned out, grain remaining in the unloader conveyor has been observed to have a tendency to settle in the enclosed lower region of the upstanding or vertical unloader conveyor section around the lower end of the auger therein and the adjacent end of the grain tank conveyor auger extending into the inlet opening. As a result, a problem that can occur if the grain tank and unloader augers are started simultaneously, or the grain tank auger is started first, is that the grain tank auger can force or pack the grain into and against the grain in the lower unloader housing, thereby causing grinding, cracking of and other damage to the grain. Also, if the augers are commonly driven and loaded with grain, the start up torque and power required will be higher than if the augers are started separately. As another problem or shortcoming, if the unloader conveyor is loaded with grain when pivoted between the sidewardly extending unloading position and the stored position, greater loads and stress are placed thereon and on the supporting structure thereof compared to if the unloader is empty. As the width of combine headers increase, it is anticipated that the length of unloader conveyors will necessarily also increase as will the amount and weight of grain remaining therein after use. As a result, the stress on the supporting structure when the unloader is in the unloading position and moving thereto and therefrom will also be increased. As still another possible problem, if the unloader auger should stall, for instance, due to a mechanical problem with the unloader drive, formation or induction of a slug of grain in the unloader tube, and the grain tank auger continues to operate, the inlet of the unloader can be packed with grain, which can result in excessive grain damage and/or damage to the grain tank auger.
Thus, what is sought is a grain tank unloader control and drive which overcomes many of the problems and shortcomings set forth above.